Urine C-peptide in relation to the degree of insulin dependence in diabetic patients.

Urine C-peptide per 24 h urine (UCPR) was assayed and correlated with the degree of insulin dependence in 324 diabetic patients. The UCPR and UCPR/weight were 74.7 +/- 26.3 micrograms/day and 1.27 +/- 0.36 micrograms/day, kg in healthy subjects, and these values were similar in diet- and sulfonylurea-treated patients. Insulin-dependent diabetics (IDDM) with history of ketosis or ketoacidosis and/or unstable plasma glucose, and patients refractory to sulfonylureas had lower UCPR values (8.5 +/- 6.6 and 22.3 +/- 14.6 micrograms/day) than the other insulin-treated patients (45.4 +/- 30.7 micrograms/day). In more than 90% of diet- and sulfonylurea-treated patients, UCPR exceeded 30 micrograms/day and UCPR/wt. exceeded 0.6 micrograms/day, kg. UCPR was less than 20 micrograms/day and UCPR/wt. less than 0.4 microgram/day,kg in more than 90% of IDDM patients, and less than 40 micrograms/day and 0.8 microgram/day,kg respectively in 80% of sulfonylurea-refractory patients. IDDM patients with more than 20 U/day of insulin doses had lower UCPR values. Longer duration of diabetes was associated with lower UCPR in IDDM patients. The results indicate that UCPR more than 30 micrograms/day or UCPR/wt. more than 0.6 micrograms/day,kg suggest non-insulin dependence, and UCPR less than 20 micrograms/day or UCPR/wt. less than 0.4 micrograms/day,kg suggest insulin dependence. Assay of UCPR provides a simple, non-invasive test for evaluating the degree of insulin dependence in diabetic patients.